Vehicles, such as rail vehicles, include power sources, such as diesel engines. In some vehicles, fuel is provided to the diesel engine by a common rail fuel system. One type of common rail fuel system comprises a low-pressure fuel pump in fluid communication with a high-pressure fuel pump, and a fuel rail in fluid communication with the high-pressure fuel pump and further in fluid communication with at least one engine cylinder. The low-pressure fuel pump delivers fuel from a fuel supply to the high-pressure fuel pump through a conduit, wherein an inlet metering valve is disposed. The high-pressure fuel pump pressurizes fuel for delivery through the fuel rail. Fuel travels through the fuel rail to at least one fuel injector, and ultimately to at least one engine cylinder. Within the at least one engine cylinder, fuel is burned to provide power to the vehicle.
Further, the higher-pressure sub-system of the common rail fuel system includes a pressure limiting valve for relieving pressure. The pressure limiting valve may redirect fuel away from the fuel rail, to the fuel supply, during a high-pressure surge (excess pressure). During the high-pressure surge, the pressure limiting valve will open in order to decrease the rail pressure. The pressure limiting valve closes when the rail pressure returns to a lower pressure than the rail pressure that originally triggered the pressure limiting valve opening. In some conditions, the rail pressure may decrease to a sufficient level for operation, yet the pressure limiting valve may remain open. In such a condition, fuel is continuously redirected to the fuel supply, resulting in decreased fuel supply pressure to the engine and possibly decreased power provided to the vehicle. Additionally, a persistently low rail pressure may signal to an Engine control unit that an external leak is present. In this example, the Engine control unit will command the engine to be disabled in order to mitigate possible effects of the presumed external leak, such as engine performance degradation. However, in fact, the shutdown may be unnecessary as the pressure limiting valve is the cause of the low rail pressure, not an external leak.